Switched filterbanks are typically used in transceivers for pre-selection or post-selection of signals or channels. Filterbanks are typically constructed with a bank of discrete filters with a switch matrix to select the filter of choice. Filters are typically sub-octave and used to enhance receiver (RX) selectivity by rejecting unwanted signals at image frequencies and other points of spurious sensitivity. On the transmitter (TX) side, filters are used to reject unwanted spurious and harmonics prior to final amplification through a power amp stage. Physical implementation of switched filterbanks typically involve a 1:N switchbank, a bank of N discrete filters, and a N:1 switchbank. A typical planar implementation has significant area allocated to the switchbanks and filters. Much area is allocated to electrical isolation requirements and isolation grounding. The cost associated with discrete filters is substantially high. These filters are typically purchased as separate surface mount components, either as lumped element or ceramic resonator topologies.
Distributed filters designed on a radio frequency (RF) printed wiring board (PWB) employ a top microstrip layer that are typically quite large and very sensitive to cavity effects, necessitating isolation walls. Distributed stripline filters are difficult to build into standard RF PWB stackups without grossly driving up costs.